Dispersants are substances which facilitate the dispersion of particles in a medium by reducing the interfacial tension between the two components. Dispersants are generally surfactants of anionic, cationic and nonionic structure. A dispersant significantly reduces the work involved in dispersion. Under the effect of mutual attraction forces, dispersed solids can tend to re-agglomerate after the dispersion process. The use of dispersants also counteracts the tendency of the solids to re-agglomerate. The dispersant used has to meet particularly stringent requirements in the dispersion of pigments, such as colored or magnetic pigments. Inadequate dispersion is reflected in an increase in the viscosity of liquid systems, in losses of brilliance and in changes of shade.
Particularly good dispersion of the colored pigment is required in the case of inks for use in inkjet printers (inkjet inks) in order to guarantee unhindered passage of the colored pigment particles through the jets of the printing head which are often only a few micrometers in diameter. In addition, the pigment particles have to be prevented from agglomerating and thus blocking the printer jets in those periods when the printer is not in operation.
Particularly good dispersion of the colored pigments is also important in the coating of hard surfaces.
EP-B-610 534 describes modified copolymers as pigment dispersants for water-based coating compositions.
WO 00/17250 describes dispersants obtained by reaction of isocyanates with certain polymeric compounds terminated at one end of the chain by special reactive groups.